Magnetic torque sensor including integral sub-unit

ABSTRACT

A pair of magnetic flux collecting rings and a magnetic sensor are integrally covered by a molded resin to form a sub unit of a torque sensor. The pair of rings and sensors are integrated and are in contact with each other, i.e., the magnetic sensor is held in between respective magnetic flux collecting portions of the rings without any air gap formed therebetween. Magnetic flux collected by the rings can be detected by the magnetic sensor to a maximum degree, whereby the signal output of the magnetic sensor is enhanced and made stable.

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon, claims the benefit of priority of, andincorporates by reference the contents of prior Japanese PatentApplication No. 2002-61260 filed on Mar. 7, 2002, and No. 2002-283425filed on Sep. 27, 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a torque sensor for detecting torqueapplied to a rotating shaft based on measurement of changes in magneticflux density or magnetic field intensity.

2. Description of the Related Art

The present inventors have filed a prior patent application relating toa torque sensor (Japanese Patent Application No. 2001-316788, U.S.Patent Application Publication No. 2002-189371). This torque sensorgenerally includes a torsion bar connecting an input shaft and an outputshaft, a multi-pole magnet fixed to one end of this torsion bar, a pairof multi-pole yokes fixed to the other end of the torsion bar anddisposed inside a magnetic field generated by the multi-pole magnet, apair of magnetic flux collecting rings for introducing magnetic fluxfrom the multi-pole yokes, and a magnetic sensor for detecting magneticfield intensity via the rings.

The pair of magnetic flux collecting rings are each provided withportions that have the function of collecting magnetic flux directedfrom the multi-pole yokes, and these portions are arranged opposite toeach other. The magnetic sensor is interposed between these mutuallyopposing magnetic flux collecting portions of the rings. When thetorsion bar is twisted, magnetic flux is generated between the pair ofmulti-pole yokes due to a change in the relative positional relationshipbetween the multi-pole magnet and multi-pole yokes in thecircumferential direction. The magnetic flux is collected by the pair ofrings, and the magnetic sensor detects the density of the magnetic flux.

It is crucial, in this torque sensor, to utilize the magnetic fluxcollected by the rings as much as possible. However, because themagnetic sensor is interposed between the magnetic flux collectingportions of the rings, there exists a problem of magnetic flux leakagethrough the inevitable air gaps between the magnetic sensor and magneticflux collecting portions. This leakage causes a decrease in signaloutput from the sensor.

Another problem is that, since the air gaps in each and every productcannot possibly be made constant because of slight variations resultingfrom assembling tolerances, the signal output from the sensors tends tobe slightly different.

SUMMARY OF THE INVENTION

The present invention has been devised taking into consideration theabove circumstances, its object being to provide a torque sensor capableof enhanced and stable signal output, which is achieved by minimizingmagnetic flux leakage.

To achieve the above object, the present invention provides a torquesensor including a torsion bar coaxially connected at opposite ends to afirst shaft and a second shaft for converting torque applied betweenboth shafts into a torsional displacement. Also provided are: amulti-pole magnet fixed to the first shaft or one end of the torsionbar, a multi-pole yoke fixed to the second shaft or the other end of thetorsion bar for forming a magnetic circuit within a magnetic fieldgenerated by the multi-pole magnet, a pair of magnetic flux collectingmembers for collecting magnetic flux from the multi-pole yoke, and amagnetic sensor for detecting magnetic field intensity via the pair ofmagnetic flux collecting members. The characteristic feature of thistorque sensor is that the magnetic sensor and the pair of magnetic fluxcollecting members are assembled as one piece.

This construction enables the air gaps between the magnetic fluxcollecting members and magnetic sensor to be minimal, whereby themagnetic sensor can maximally detect collected magnetic flux.

In the above torque sensor, the magnetic sensor and the pair of magneticflux collecting members may integrally be covered by a molded resin, anda signal cable from the magnetic sensor and a terminal connected to thesignal cable may be embedded in the molded resin. This constructionintegrates the magnetic sensor, the pair of magnetic flux collectingmembers, and the terminal by the molded resin, thereby facilitatingassembly of these components to a housing or the like. In the moldedresin, a connector for holding the terminal may also be integrallyprovided, thereby facilitating assembly.

Alternatively, the torque sensor may have a lead wire for an externalelectrical connection of the terminal, one end of which lead wire isembedded in the molded resin and connected to the terminal inside themolded resin. A reduction in cost can be achieved by the omission of theconnectors.

The pair of magnetic flux collecting members may be formed either in aring shape or in a semicircular shape. Ring-shaped magnetic fluxcollecting members will prevent a displacement of their axial centersrelative to the multi-pole yokes, and thus can reduce detecting errorsof the magnetic sensor. The semicircular design will offer better andeasier assembly, since it allows assembly along a radial direction.

The pair of magnetic flux collecting members and the magnetic sensor mayseparately be molded of resin and assembled as one piece. Thisconstruction will facilitate the positioning of the magnetic fluxcollecting members and magnetic sensors relative to each other.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1A is a cross-sectional view of a sub unit of a torque sensoraccording to a first embodiment of the present invention;

FIG. 1B is a cross-sectional view of a sub unit of a torque sensoraccording to a first embodiment of the present invention;

FIG. 2A is a diagram for explaining the operation of the torque sensor;

FIG. 2B is a diagram for explaining the operation of the torque sensor;

FIG. 2C is a diagram for explaining the operation of the torque sensor;

FIG. 3 is a cross-sectional view of the entire torque sensor;

FIG. 4 is a schematic illustration of an electric power steering system;

FIG. 5A is a cross-sectional view of a sub unit of a torque sensoraccording to a second embodiment of the present invention;

FIG. 5B is a cross-sectional view of a sub unit of a torque sensoraccording to a second embodiment of the present invention;

FIG. 6A is a cross-sectional view of an assembly of a magnetic sensorand a pair of magnetic flux collecting rings integrated with each otheraccording to a third embodiment of the present invention;

FIG. 6B is a cross-sectional view of an assembly of a magnetic sensorand a pair of magnetic flux collecting rings integrated with each otheraccording to a third embodiment of the present invention,

FIG. 6C is a plan view of the assembly as viewed from the side of themagnetic sensor;

FIG. 7A is a cross-sectional view of a resin molded magnetic sensor;

FIG. 7B is a front view of a resin molded magnetic sensor;

FIG. 7C is a cross-sectional view of resin molded magnetic fluxcollecting rings according to the third embodiment;

FIG. 7D is a front view of resin molded magnetic flux collecting ringsaccording to the third embodiment; and

FIG. 8 is a cross-sectional view of the entire torque sensor accordingto the third embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be hereinafterdescribed with reference to the accompanying drawings. The followingdescription of the preferred embodiments is merely exemplary in natureand is in no way intended to limit the invention, its application, oruses.

(First Embodiment)

FIG. 1A and FIG. 1B are cross-sectional views of a sub unit 4 used in atorque sensor 1 including a magnetic sensor 2 and a pair of magneticflux collecting rings 3 according to a first embodiment of the presentinvention.

The torque sensor 1 of this embodiment is employed, for example, in anelectric power steering system for a vehicle shown in FIG. 4, fordetecting steering power or torque applied to the shaft of the steering5, and outputting the detected torque to an electric control unit (ECU)6. The ECU 6 controls output of an electric motor 7 according to thesteering power detected by the torque sensor 1.

As shown in FIG. 3, the torque sensor 1 is disposed between an inputshaft 8 and an output shaft 9 that constitute the steering shaft. Thetorque sensor 1 is comprised of a torsion bar 10, a multi-pole magnet11, a pair of multi-pole yokes 12, a pair of magnetic flux collectingrings 3, and a magnetic sensor 2.

The torsion bar 10 is a bar-like resilient member, and its oppositeaxial ends are fixed to the input shaft 8 and output shaft 9 by pins 13,respectively. Application of steering torque to the steering shaftproduces a torsional displacement in the torsion bar 10 according to thetorque. The multi-pole magnet 11 is formed in a ring shape and composedof North and South poles alternately arranged in a circumferentialdirection. The multi-pole magnet 11 is press-fitted and fixed to anouter circumference of either the input shaft 8 or the output shaft 9.

The pair of multi-pole yokes 12 are ring-shaped and made of a softmagnetic material. They each have a plurality of circumferentially,equally spaced claws 12 a, and are arranged such that their respectiveclaws 12 a engage with each other with an air gap between them, as shownin FIG. 2B. The pair of multi-pole yokes 12 are disposed close to theouter circumference of the multi-pole magnet 11, and fixed to either ofthe input shaft 8 or the output shaft 9 by a holder 14.

The multi-pole yokes 12 (12A, 12B) are positioned relative to themulti-pole magnet 11 such that, when the torsion bar 10 is not twisted,each axial center of the claws 12 a of the multi-pole yokes 12 (12A,12B) coincides with a boundary between immediately adjacent North andSouth poles of the multi-pole magnet 11 as shown in FIG. 2B. Thus, theoutput voltage of the magnetic sensor 2 is zero when no steering poweris applied between the input shaft 8 and output shaft 9.

The pair of magnetic flux collecting rings 3 are made of the same softmagnetic material as the multi-pole yokes 12 and are disposed close tothe outer circumference of the multi-pole yokes 12. The rings 3 have thefunction of collecting magnetic flux from the multi-pole yokes 12. Theyare provided with respective plate-like magnetic flux collectingportions 3 a at one location in the circumferential direction, which arearranged opposite to each other. The magnetic sensor 2 is interposedbetween these magnetic flux collecting portions 3 a of the pair of rings3 for detecting the density of magnetic flux generated therebetween.

The magnetic flux collecting rings 3 and magnetic sensor 2 areintegrally covered by a molded resin 15 to form the sub unit 4 as shownin FIG. 1A and FIG. 1B, which is assembled to a column housing 16 thatsupports the steering shaft from an axial direction (see FIG. 3). Therings 3 and sensor 2 are integrated such that the magnetic sensor 2 isinterposed between the magnetic flux collecting portions 3 a of therings 3 without any gap therebetween, i.e., they are in close contactwith each other.

The sub unit 4 includes a terminal 17 that is connected to a signalcable 2 a of the magnetic sensor 2 and embedded in the molded resin 15.A connector 18 for holding the terminal 17 is also provided integrallyin the molded resin 15.

The torque sensor of this embodiment operates as follows:

When no steering torque is applied to the torsion bar 10, there is notorsional displacement in the torsion bar 10. In this state, each axialcenter of the claws 12 a of the multi-pole yokes 12 coincides with eachboundary between immediately adjacent North and South poles of themulti-pole magnet 11, as shown in FIG. 2B. The number of magnetic forcelines extending from each of the North poles of the multi-pole magnet 11to each of the claws 12 a of the multi-pole yokes 12 is equal to that ofthe magnetic force lines extending from each of the South poles to eachof the claws 12 a. These magnetic force lines form closed loops,respectively, inside each of the pair of multi-pole yokes 12A, 12B, anddo not leak into the air gap between both yokes. Thus the output of themagnetic sensor 2 is zero at this time.

When steering torque is input to the steering shaft, causing a torsionaldisplacement in the torsion bar 10, the relative positions of themulti-pole magnet 11 and the pair of multi-pole yokes 12 are changed ina circumferential direction. The circumferential displacement betweeneach of the axial centers of claws 12 a and the boundary betweenadjacent North and South poles of the multi-pole magnet 11 causes anincrease in the number of magnetic force lines of opposite polarity ineach of the multi-pole yokes 12A, 12B. Magnetic fluxes of oppositepolarity are thus generated between both yokes, which are directed bythe rings 3 into their magnetic flux collecting portions 3 a, and thesensor 2 detects the density of magnetic flux between the magnetic fluxcollecting portions 3 a.

As described above, the torque sensor 1 of this embodiment has a subunit 4 made up of a magnetic sensor 2 and a pair of magnetic fluxcollecting rings 3 integrated therewith. Since the sensor 2 isinterposed between the magnetic flux collecting portions 3 a of therings 3 in contact therewith, there is no air gap formed between thesensor 2 and magnetic flux collecting portions 3 a. Therefore, thecollected magnetic flux can maximally be detected by the magnetic sensor2. The sub unit 4 thus contributes to more stable and enhanced signaloutput of the magnetic sensor 2.

The sub unit 4 also provides a design for ease of assembly to the columnhousing 16 or the like as compared to a conventional torque sensor,because it enables the pair of magnetic flux collecting rings 3 andmagnetic sensor 2 to be readily assembled to the column housing 16 froman axial direction as shown in FIG. 3.

Another advantage of the sub unit 4 is that, since it includes theterminal 17 and the connector 18 for retaining the terminal 17 that areboth embedded in the molded resin 15, it enables several relevantcomponents such as rings 3, sensor 2, terminals 17, and connectors 18 tobe handled as one component, thus facilitating management of components.

(Second Embodiment)

FIG. 5A and FIG. 5B are cross-sectional views of a sub unit 4 of atorque sensor according to a second embodiment of the present invention.The magnetic flux collecting rings 3 in this sub unit 4 are formed in asemicircular shape as can be seen from the drawings. This configurationenables the sub unit 4 to be assembled to the column housing 16 not onlyfrom an axial direction but also from a radial direction. It offers evenbetter assembly of the sub unit 4 and allows more freedom of design forthe column housing 16 and surrounding components.

The rings 3, even in their semicircular form, can exhibit equal magneticflux collecting properties for directing magnetic flux from themulti-pole yokes 12. The sub unit 4 of this embodiment employs a leadwire 19 instead of the connector 18 in the previous embodiment. One endof the lead wire 19 is embedded in the molded resin 15 and is connectedto the terminal 17 inside the molded resin 15. This results in a costreduction because the connectors 18 are omitted.

(Third Embodiment)

FIG. 6A and FIG. 6B are cross-sectional views of an assembly of amagnetic sensor 2 and a pair of magnetic flux collecting rings 3integrated therewith according to a third embodiment of the presentinvention. FIG. 6C is a top, plan view of the assembly viewed from theside of the magnetic sensor 2.

In this embodiment, the magnetic sensor 2 and the pair of magnetic fluxcollecting rings 3 are each resin molded before being assembled into onepiece. Two sensors 2 are arranged side by side and the portionsconnected to their respective lead wires 19 are resin molded as shown inFIG. 7B. The sensor mold 20, which is the resin molded portion of thesensors, is formed in an L-shape in cross section and has a seat portion20 a and a back portion 20 b as shown in FIG. 7A. The two magneticsensors 2 project from a bottom face of the seat portion 20 a, and theends of the lead wires 19 extend from a top end face of the back portion20 b.

The pair of rings 3 are arranged such that their magnetic fluxcollecting portions 3 a face each other as shown in FIG. 7C, and theouter circumferential sides of the rings are resin molded. The mold 21covers only the outer side and their inner circumferential side isexposed. The mold 21 includes a holder portion 21 a and a snap fitportion 21 b for holding the sensor mold 20 and a hole 21 c foraccommodating the magnetic sensors 2.

The holder portion 21 a consists of a pair of extended bars spaced aparta certain distance on an outer circumference of the mold 21. In an innerface of the mutually facing bars of the holder portion 21 a are formedguide grooves 21 d for guiding the back portion 20 b of the sensor mold20.

The snap fit portion 21 b also consists of a pair of bars similarly tothe holder portion 21 a, that protrude on an outer circumference of themold 21. They are given a certain resiliency, and provided with hooks 21e as shown in FIG. 7D at their distal ends, for engaging with the seatportion 20 a of the sensor mold 20 when the ring component is assembledto the sensor component.

The hole 21 c communicates to a space between the mutually facingmagnetic flux collecting portions 3 a of the pair of rings 3, as shownin FIG. 7C. The distance between the mutually facing magnetic fluxcollecting portions 3 a is designed such as to give a certain clearancebetween these portions and the magnetic sensors 2.

When the ring component and sensor component are assembled into onepiece, the magnetic sensors 2 are accommodated in the space between theopposing magnetic flux collecting portions 3 a of the pair of rings 3,with the back portion 20 b of the sensor mold 20 held by the holderportion 21 a and the seat portion 20 a of the sensor mold 20 retained bythe snap fit portion 21 b, as shown in FIG. 6B and FIG. 6C. Thisassembly, made up of the integrated rings 3 and sensors 2, is insertedand tightly held, as shown in FIG. 8, between a column housing 16 asupporting the input shaft 8 and another column housing 16 b supportingthe output shaft 9.

According to the construction of this embodiment, since the pair ofrings 3 and magnetic sensors 2 are integrated into a one-piece assembly,they can readily be positioned relative to each other. That is, themagnetic sensors 2 can be arranged at a predetermined location in thespace between the two mutually facing magnetic flux collecting portions3 a of the rings 3 simply by inserting them into the hole 21 c formed inthe mold 21 covering the rings 3.

Similar to the first embodiment, there is practically no air gap formedbetween the magnetic sensors 2 and the magnetic flux collecting portions3 a of the rings 3. Therefore, the collected magnetic flux can bedetected by the magnetic sensors 2 to a maximum degree.

The description of the invention is merely exemplary in nature and,thus, variations that do not depart from the gist of the invention areintended to be within the scope of the invention. Such variations arenot to be regarded as a departure from the spirit and scope of theinvention.

1. A torque sensor comprising: a torsion bar connected at its oppositeends to a first shaft and a second shall for converting torque appliedbetween the first shaft and the second shaft into a torsionaldisplacement; a multi-pole magnet fixed to either one of said shafts anda first end of said torsion bar; a multi-pole yoke fixed to either oneof said shafts and a second end of said torsion bar for forming amagnetic circuit within a magnetic field generated by said multi-polemagnet; a pair of magnetic flux collecting members for collectingmagnetic flux from the multi-pole yoke; and a magnetic sensor fordetecting magnetic field intensity via said pair of magnetic fluxcollecting members, wherein said magnetic sensor and said pair ofmagnetic flux collecting members are assembled as one piece.
 2. Thetorque sensor according to claim 1, wherein said magnetic sensor andsaid pair of magnetic flux collecting members are integrally covered bya molded resin, and wherein a signal cable from said magnetic sensor anda terminal connected to the signal cable are embedded in said moldedresin.
 3. The torque sensor according to claim 2, wherein said moldedresin contains a connector for holding said terminal.
 4. The torquesensor according to claim 2, further including a lead wire for anexternal electrical connection of said terminal, wherein one end of thelead wire is embedded in said molded resin and connected to saidterminal inside said molded resin.
 5. The torque sensor according toclaim 1, wherein said pair of magnetic flux collecting members areformed in either one of a ring shape and a semicircular shape.
 6. Thetorque sensor according to claim 2, wherein said pair of magnetic fluxcollecting members are formed in either one of a ring shape and asemicircular shape.
 7. The torque sensor according to claim 3, whereinsaid pair of magnetic flux collecting members are formed in either oneof a ring shape and a semicircular shape.
 8. The torque sensor accordingto claim 4, wherein said pair of magnetic flux collecting members areformed in either one of a ring shape and a semicircular shape.
 9. Thetorque sensor according to claim 1, wherein said pair of magnetic fluxcollecting members and said magnetic sensor are separately resin moldedand assembled as one piece.
 10. A torque sensor comprising: a torsionbar connected at its opposite ends to a first shaft and a second shaftfor converting torque applied between the first shaft and the secondshall into a torsional displacement: a multi-pole magnet fixed to eitherone of said shafts and a first end of said torsion bar; a multi-poleyoke fixed to either one of said shafts and a second end of said torsionbar for forming a magnetic circuit within a magnetic field generated bysaid multi-pole magnet; a pair of magnetic flux collecting members forcollecting magnetic flux from the multi-pole yoke; and a magnetic sensorfor detecting magnetic field intensity via said pair of magnetic fluxcollecting members, wherein said magnetic sensor and said pair ofmagnetic flux collecting members are constructed in one piece.
 11. Thetorque sensor according to claim 10, wherein said pair of magnetic fluxcollecting members are formed in either one of a ring shape and asemicircular shape.
 12. A torque sensor comprising: a torsion barconnected at its opposite ends to a first shaft and a second shaft forconverting torque applied between the first shaft and the second shaftinto a torsional displacement; a multi-pole magnet fixed to either oneof the shafts and a first end of the torsion bar; a multi-pole yokefixed to either one of the shafts and a second end of the torsion barfor forming a magnetic circuit within magnetic field generated by themulti-pole magnet; a pair of magnetic flux collecting members forcollecting magnetic flux from the multi-pole yoke; and a magnetic sensorfor detecting magnetic field intensity via the pair of magnetic fluxcollecting members, wherein the magnetic senor and the pair of magneticflux collecting members are integrally connected to form a singlesub-unit in which the relative positions of the magnetic sensor and thepair of magnetic flux collecting members are constant during assembly ofthe torque sensor.
 13. The torque sensor according to claim 12, whereinthe pair of magnetic flux collecting members are formed in either one ofa ring shape and a semicircular shape.